It might not be obvious at first glance why taxonomies are important to storytelling and social media, but the more you work with the concepts, the more critical some kind of knowledge structure seems. 

In capturing knowledge from the flow of blog posts and messages, we're imposing structure on a particular subset of the conversation.  If the microcontent flow becomes substantial, and the narratives being created are important to you, then you will  need a way to manage that stream of  material, or drown. 

People are struggling with two aspects of the flow.  One is the enormous diversity of sources.  Twitter's list function is just an example of a growing number of applications people are using to manage their ever-expanding network of potential sources of content.  The second is the even more daunting number of individual chunkis of microcontent ... posts, links, photos, videos, etc.  Digg for the general public, and mendeley and zotero on the specialist side, are examples of applications that try to manage that flood.  And of course many applications have some form of tagging.

Interestingly, one of the first things people want to do when they create a taxonomy is share it.  A taxonomy is of recognized value; someone you know and presumably trust has put a lot of effort into adding a layer of editorial content to the flow, which can then be incorporated into your own evolving knowledge structure.  There's been a lot of discussion over the last few years about "folksonomies", taxonomies that bubble up from large communities, as a result of tagging and shared metadata.

But I believe we're just in the first stages of the evolution and adoption of taxonomies and related tools in relationship to social media, story and knowledge capture.  Taxonomies and ontologies and other concepts from knowledge management have their complexities and hierarchies of value.  People are learning by doing, and there's a also a lot to learn about the relationship of personal to group, community, and organizational taxonomies.  There's going to be much more discussion (and new tools and applications!) in this area in the next few years.

One group that's been thinking a great deal about these issues Earley and Associates. Here's a presentation by Stephanie Lemieux about combining personal and group taxonomies: